Friday 5: 5 Steps to a Native Bee Cavity Nest

I quite enjoyed writing the bee nest cap post last week, so I’m going to do another Friday 5 about my bees!  This week I am focusing on how the bees (Megachile sp.) are making their nests.  It involves these 5 steps:

1. Find a cavity

finding nest

Finding a nest

My bee house was designed to provide cavities to attract native cavity nesting bees and it seems to being doing its job!  At any given time in the last month, there have been bees looking for nesting sites.  They fly around in front of the bee house (like the bee in the lower center of the photo), find a cavity that looks good, and crawl inside to inspect it.  If it is acceptable, they fly off and start gathering nesting materials.  If they don’t like it, they fly around and look for a better cavity.

2.  Build and provision a cell

building a cell

An incomplete cell

After a suitable cavity is selected, the bee starts building cells in her new nest.  She flies away from the nest and returns a few minutes later with leaf bits, small rocks, and globs of resin in her mouth.  She crawls into the nest head first and starts plastering the walls with the nesting materials.  On most trips into the cavity, she carries a load of bright yellow pollen on the underside of her abdomen.  Presumably, she deposits the pollen inside the cell for the future larvae to eat because the bees nearly always come out of the nests clean.  When the cell is about 8 – 10 mm long, they move on to the next step.

3. Lay eggs

laying eggs

Bee looking out after laying eggs

After a cell is completed, the bee crawls all the way out of the nest, turns around, and backs into the nest.  She spends several minutes inside the nest laying eggs in this position.  When she’s done, she crawls to the front of the nest, pauses for a minute or so, and flies off to start gathering nesting materials for the next step.

4. Cap cell and repeat

capping a cell

Capping a cell

When the bee returns to her nest after laying eggs, she appears with more nesting materials in her mouth, but no pollen.  She then builds a cap for the cell in which she has laid her eggs using the nesting materials.  There is a similar wall between every individual cell within the nest.

The bees typically make about 8 cells in the cavities in my bee house. Once a cell is sealed, the bee starts a new cell, lays more eggs, and caps the new cell.  It’s taking my bees 2-5 days to complete all of their cells, depending on the diameter of the hole and the length of the cavity.  The bigger the diameter, the longer the bee takes to build her complete nest.

5. Cap nest

building a nest cap

Building a nest cap

When cavity is nearly full of cells and there is only about 0.5 – 1 cm of the cavity still empty, the bee starts to build her nest cap.  She carries leaf bits, rocks, and resin to the nest and starts packing the materials in front of the last cell, often leaving a space between the last cell and the nest cap.  She starts building with a mixture of what is apparently leaves and saliva, then starts adding sand, rocks, and resin closer to the end of the cavity.  Depending on the nest cap type she builds, the bee may build out beyond the cavity 3 – 5 mm, but many of them are finished flush with the edge of the nest.  Most of the bees start a new nest almost immediately after finishing one, often moving into the next closest available and suitable cavity.

I have to say that I’m rather addicted to watching my bees.  I gave myself a sunburn one day because I was out photographing the bees building their nests for so long.  Another day I stepped into one of the many ant nests in my yard because I was so absorbed by the bees (have I mentioned lately that ants and I don’t get along?)  One day it was so windy I was worried another branch like the one I used to build my bee house would break off the tree and smack me in the head.  Still, I go out every day and watch.  I’m mean really, who can resist this?:

giant resin glob

Giant resin glob!

Look how big that resin glob is compared to the bee!  Anything that puts so much work into building a nest while looking so darned cute is alright in my book.  :)


Unless otherwise stated, all text, images, and video are copyright © 2011

Friday 5: Leafcutter Bee Nest Caps

The bee house I put up in my yard in mid-April has been a complete success!  Nearly every cavity has been filled with nesting materials and eggs and now I’m waiting for the new bees to emerge.  I’ve watched them obsessively and am keeping hard-core notes about the whole process, so I am totally in love with my bees!  One thing that has fascinated me is the variety in the capping stuctures and materials used among cavities.  To the best of my knowledge, all of my bees are these:


A leafcutter bee (Megachile) bee making a nest

They’re a species of leafcutter bee in the genus Megachile.  Even though they’re apparently all the same species, they’re still building their nests according to… something!  Maybe it’s individual preferences or access to the building materials that controls it, but three different caps might be built by three different bees on the same day.  Fascinating!  My bees have been spending 2-3 days busily building their nests and laying eggs and then spend part of a day building a cap to seal everything safely inside.  They’ve made 5 different types of caps so far, perfect for Friday 5!

Resin Caps

resin cap

Resin caps

The first several bees made these caps.  Then they stopped making them.  Most recently, bees have been STEALING the resin from the completed resin caps, cutting pieces away from the caps and hauling them off, and then recapping the nests with mud.  Odd!  I assume there’s a resin shortage now and they’re scrambling to find it wherever they can.  When the bees build this kind of cap, they bring big globs of it from somewhere on the other side of my house, then stretch it across the opening.  (The bee in the photo at the top has a big glob of it in her jaws, ready to stick it onto the cap.)  Then they pile a bunch more on the front, making a thick, flexible cap.  They smell awesome too!  You can smell the resin from several feet away.  Reminds me of vacations in the pine topped mountains in Colorado…

Leaf Caps

Chewed leaf cap

Leaf cap, in progress. (This one is still green, even though it's now dry.)

Some of the caps, though not many, are made of chewed leaf bits.  The bees bring in large pieces of leaves or flower petals or other plant materials, then chew them up and stick them onto the nest.  Presumably they are sticking the leaf fragments together with saliva.  The best thing about the leaf caps is the variation in color!  Most of them are green like this one, but I have one yellow, one purple, and one vivid red one too.  Awesome!

Rock Caps

Rock cap

Rock cap

These seem to be the least popular choice, but there are a few.  The bees use resin to attach little pebbles (which they collect from the corner of my yard) onto the front of their nests.  After they build up a few layers of rocks, they call it good and either start a new nest in another hole or fly away.  I love watching the bees make these caps!  There’s something about a bee flying around with a rock nearly the size of her head clamped in her mouth that is both inspiring and terribly entertaining.

Flat Mud Caps

Flat mud cap

Flat mud cap

The mud caps are very popular with the bees in my bee house and they take one of two forms.  The flat mud caps are built so that the outer edge is flush with the face of the log in which the cavity is located.  After they dry a bit, they tend to sink inward in the middle a little, giving them a gentle concave look.  To the best of my knowledge, the bees are making the mud themselves by carrying little piles of dirt from another part of my yard, mixing it with saliva and chewed leaf bits, and then spreading the whole mess across the nest entrances.

Round Mud Caps

Round mud cap

Round mud cap

This was the last style of cap to appear in my bee house, but they look really fabulous!  The round mud caps are a sort of mixture of the flat mud cap and the rocks cap.  The bees stick a bunch of little rocks onto the front of the nest, building out past the edge of the log.  Then they plaster over the whole thing with mud as in the flat mud cap.  The result is a cap that extends well beyond the nest entrance, almost like the little developing bees inside are blowing bubbles in the mud!

Watching my bees has been great and I’m very pleased my bee house has worked as well as it has.  And just look at all the individual choices being made by the bees!  Fabulous.  I’m definitely going to make myself some new bee houses (even bought a new power tool – my first circular saw – to do it!) because it’s been great fun watching them build their nests.  I highly recommend the experience!


I am going to do my best to get a blog post up on Monday, but there’s a good chance it won’t happen.  I am leaving town for a family emergency today and that is a lot more important than getting a blog post out on time.  I will be back, and as soon as I can, but if you don’t hear from me for a while that’s why.


Unless otherwise stated, all text, images, and video are copyright © 2011